The neglected puzzle of dementia in people with severe/profound intellectual disabilities: A systematic literature review of observable symptoms.
Maureen B G Wissing, Aurora M Ulgiati, Johannes S M Hobbelen and 3 others
PMID 34219327WHAT IT FOUND
Diagnosing dementia in severe intellectual disability requires watching for behaviour changes, not cognitive tests.
Key signs include withdrawal, aggression, sleep issues, and loss of self-care skills. Standard cognitive assessments are often impossible due to low baseline function, so caregiver observation of these behavioural shifts is essential.
Key findings
01Standard neuropsychological tests are often unusable for people with severe/profound intellectual disabilities due to floor effects, making direct cognitive assessment impossible.
02Behavioural and psychological symptoms, specifically withdrawal, aggression, irritability, and sleep disturbances, are the primary observable indicators used to identify dementia in this population.
03Loss of previously acquired self-care skills and a decline in mobility or gait are reported physical and functional changes associated with dementia in this group.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
The review identified only 11 studies, with very small sample sizes in the dementia-specific studies (ranging from 1 to 6 individuals per study). The intellectual disability levels were classified inconsistently across studies, with some not specifying how levels were determined. The exact type of dementia (e.g., Alzheimer's vs. vascular) was not reported in many studies, making it difficult to distinguish symptom patterns. The review did not include a risk of bias assessment for the included studies. Many studies relied on case files or informant reports, which may be subject to recall bias or misattribution of symptoms to ageing rather than dementia.
Declared interests
No specific conflicts of interest or funding sources were mentioned in the provided text.
The easy way to misread this
Do not assume that a lack of measurable cognitive decline on standard tests rules out dementia. In people with severe/profound intellectual disabilities, floor effects often make these tests impossible to use, so diagnosis must rely on behavioural and functional changes.